# Patent

## Title
Communication system to which multiple access control method is applied

## Abstract

A communication system CS includes a plurality of communication stations and data communication is performed between any two communication stations, one is a transmitting station and the other is a receiving station. When any data for transmission is generated, the transmitting station transmits, to the receiving station, a reservation request packet for requesting bandwidth reservation. The receiving station reserves a bandwidth responding to the reservation request packet and then transmits a communication reservation packet to inform the transmitting station of the reserved bandwidth. The transmitting station creates a data packet and then transmits the created data packet through the informed bandwidth. The receiving station stores a valid period of the bandwidth reserved for the transmitting station, and voluntarily and repeatedly creates, for transmission, the communication reservation packet for the duration of the stored valid period. Accordingly, a communication system in which time for bandwidth reservation is shortened and thus bandwidths are effectively utilized is implemented.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to communication systems, and more particularly to a communication system in which a transmitting station and a receiving station are communicably connected through a transmission path, and the receiving station reserves a bandwidth, which is used in data communication, for the transmitting station in advance.
2. Description of the Background Art
Conventionally, a multiple access method has been applied to some communication systems. As an example thereof, “Splid-channel Reservation Multiple Access” (IEEE Trans. Commun., vol. COM-24, pp. 832 to 845, August 1976) is described next below by referring to FIG. 16. The communication system shown in FIG. 16 includes a central station 121, which controls bandwidths for communication, and secondary stations 122 and 123. Hereinafter, a description is made for a case where the secondary stations 122 and 123 transmit data to the central station 121.
For data transmission, the secondary stations 122 and 123 first transmit request packets 124 and 125 to the central station 121 using a reserved channel. After receiving the request packets 124 and 125, the central station 121 schedules timing for data packet transmission so as to reserve bandwidths for the secondary stations 122 and 123. And then, the central station 121 creates a response packet 126 for transmission to a channel for response.
The secondary stations 122 and 123 respectively receive and analyze the response packet 126 to find which bandwidths are each assigned thereto. Through the assigned bandwidths, the secondary stations 122 and 123 respectively transmit data packets 127 and 128 created in accordance with data.
In such SRMA (Splid-channel Reservation Multiple Access), it is necessary to reserve the bandwidth for every data packet in advance to transfer the same. In other words, data packet transmission always follows bandwidth reservation.
For bandwidth reservation, the request packets 124 and 125 and the response packet 126 are transmitted and received. The time requisite for transmission and reception thereof results in heavy overhead and bandwidth usage to a considerable degree.
Further, the stations 122 and 123 are allowed to freely send out the request packets 124 and 125 to any channel for reservation. Accordingly, the request packets 124 and 125 may come into communication collision with each other if being transmitted with the same timing.
If this is the case, the central station 121 cannot correctly receive the collided request packets 124 and 125, and thus cannot create the response packet 126 for transmission. Therefor, the stations 122 and 123 are required to transmit the once-transmitted request packets again, thereby rendering the data communication delayed.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to implement a communication system in which bandwidths are effectively utilized by reducing time for bandwidth reservation.
Another object of the present invention is to implement a communication system in which time between generating and transmitting data is shortened.
A first aspect of the present invention is directed to a communication system in which a transmitting station and a receiving station are communicably connected through a transmission path, and the receiving station reserves a bandwidth used in data communication for the transmitting station in advance, wherein the transmitting station transmits a reservation request packet for bandwidth reservation to the receiving station when data to be transmitted is generated, the receiving station reserves the bandwidth in response to the reservation request packet from the transmitting station, and transmits a communication reservation packet for informing the transmitting station of the reserved bandwidth, the transmitting station creates a data packet according to the generated data, and transmits the created data packet through the bandwidth informed by the communication reservation packet from the receiving station, and the receiving station stores a valid period of the bandwidth reserved for the transmitting station, and voluntarily and repeatedly transmits the communication reservation packet to the transmitting station during the stored valid period.
In the conventional SRMA, a request packet corresponding to the reservation request packet and a response packet corresponding to the communication reservation packet are always exchanged immediately before data communication.
However, in the first aspect, after receiving one reservation request packet, a receiving station voluntarily and repeatedly transmits the communication reservation packet as long as the valid period is valid. In other words, a transmitting station only needs to transmit the reservation request packet once so that the once-reserved bandwidth assigned therefor is available for the duration of the valid period. In this manner, in the first aspect, the number of transmitting the reservation request packet is decreased, and accordingly the overhead can be reduced. Accordingly, it becomes possible to implement the communication system in which the bandwidths are effectively utilized.
According to a second aspect, in the first aspect, an initial value of the valid period stored for the transmitting station is predetermined, and the receiving station further shortens the stored valid period with given timing, lengthens the stored valid period on reception of the data packet from the transmitting station, deletes the valid period when the valid period is equal to a predetermined reference value, and voluntarily and repeatedly transmits the communication reservation packet to the transmitting station as long as the valid period is stored.
In the second aspect, the receiving station shortens the valid period with a predetermined timing, and lengthens it after receiving the data packet. Accordingly, the more data is transmitted from the transmitting station, the longer the valid period becomes, and vice versa. In this manner, since the bandwidth to be assigned can be changed in volume according to the volume of data transmitted in the transmitting station, and therefore the bandwidths can be effectively utilized in this communication system.
According to a third aspect, in the second aspect, the transmitting station further sets an identifier assigned thereto to the reservation request packet, and the receiving station further stores the identifier set to the reservation request packet transmitted from the transmitting station together with the initial value of the valid period, and when deletes the valid period, deletes the stored identifier together therewith.
In the third aspect, the receiving station registers the identifier and the valid period of the transmitting station as a set. In this manner, even if the communication system includes a plurality of transmitting stations, the transmitting stations can be uniquely identified. Accordingly, the communication system can employ a number of stations.
According to a fourth aspect, in the first aspect, the receiving station further transmits, with given timing, a request inquiry packet for allowing the transmitting station to transmit the reservation request packet, and the transmitting station further transmits the reservation request packet in response to the request inquiry packet transmitted from the receiving station.
In the fourth aspect, the receiving station transmits the request inquiry packet with a given timing. Therefore, the transmitting station can find, with reliability, the right time to transmit the reservation request packet.
According to a fifth aspect, in the fourth aspect, the receiving station further sets, to the request inquiry packet, a probability that the transmitting station can transmit the reservation request packet, and the transmitting station further transmits the reservation request packet according to the probability value included in the request inquiry packet transmitted from the receiving station.
In the fifth aspect, the transmitting station transmits the reservation request packet according to the probability value. To be specific, the lower the probability value becomes, it gets more difficult for the transmitting station to transmit the reserv ation request packet. Accordingly the reservation request packet hardly collides with others on the transmission path. In this manner, time taken before data packet transmission can be shorter than the conventional SRMA.
According to a sixth aspect, in the fifth aspect, when the receiving station detected a communication collision on the transmission path, the probability value set to the request inquiry packet is relatively low.
In the sixth aspect, the probability gets relatively low when any communication collision is detected on the transmission path. Accordingly, it gets more difficult for the transmitting station to transmit the reservation request packet. In this manner, at least after some communication collision is detected, the reservation request packet hardly collides with others on the transmission path.
According to a seventh aspect, in the fifth aspect, when the receiving station correctly receives the reservation request packet from the transmission path, the probability value set to the request inquiry packet is relatively high.
According to an eighth aspect, in the fifth aspect, when no signal arrives the receiving station from the transmission path for a given time period, the probability value set to the request inquiry packet is relatively high.
In a case where the receiving station correctly receives the reservation request packet, or where the receiving station has no incoming signal for a predetermined time, the transmission path is not congested. In such cases, in the seventh and eighth aspects, the probability to be set is relatively high, and it accordingly gets easier for the transmitting station to transmit the reservation request packet.
According to a ninth aspect, in the second aspect, the receiving station further changes a time interval between two communication reservation packets according to the valid period.
According to a tenth aspect, in the first aspect, the receiving station further changes a time interval between two communication reservation packets according to a transfer rate required by the transmitting station.
In the ninth and tenth aspects, a time interval between two communication reservation packets is changed according to the valid period or requiring transfer rate on the transmitting station side. In this manner, transfer rate from the transmitting station to the receiving station is varied, and thus the communication system can be provided with more flexibility.
According to an eleventh aspect, in the first aspect, when no signal arrives the receiving station from the transmission path for a given time period, the receiving station further judges that the communication reservation packet can be transmitted.
According to a twelfth aspect, in the first aspect, the receiving station further judges that the communication reservation packet can be transmitted on reception of the data packet from the transmission path.
According to a thirteenth aspect, in the first aspect, the transmitting station further judges that the reservation request packet can be transmitted on reception of the data packet or the communication reservation packet from the transmission path.
With each timing described in the eleventh to thirteenth aspects, the possibility for the transmission path being congested is low. Accordingly, the data packet or the reservation request packet transmitted from the transmitting station or the receiving station hardly collides with others on the transmission path.
According to a fourteenth aspect, in the first aspect, when no signal arrives the receiving station from the transmission path for a given time period, the transmitting station further judges that the reservation request packet can be transmitted.
According to a fifteenth aspect, in the first aspect, the transmitting station further judges that the data packet can be transmitted on reception of another data packet from the transmission path.
According to a sixteenth aspect, in the first aspect, the transmitting station further measures a lapse of time after transmitted the data packet, and when the lapse of time becomes equal to a reference value relevant to the valid period, judges that the reservation request packet can be transmitted.
In the conventional SRMA, the request packet corresponding to the reservation request packet is transmitt ed via a channel for reservation.
However, in the fourteenth to six teenth aspects, the transmitting station has data for transmission and determines that the reservation request packet can be transmitted with any timing described in these aspects. To be specific, in this communication system, the transmitting station has no more need to wait for a time frame to which the channel for reservation is set. Accordingly, in the transmitting station, time between generating, the data for transmission and transmitting the reservation request packet (i.e., time before data communication) can be shortened.
Further, with each timing described in the fifteenth to seventeenth aspects, the transmission path is not so congested, because packet exchange is over. The reservation request packet being sent out from the transmitting station with such timings, it becomes possible to provide the communication system in which the bandwidths are more ef ectively utilized, a nd the transmitted reservation request packet hardly collides with others on the transmission path.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the follow ing detailed description of the present invention when taken in conjunction with the accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing the entire structure of a communication system CS according to an embodiment of the present invention;
FIG. 2 is a sequence chart roughly illustrating the first half of a communication procedure carried out in the communication system CS in FIG. 1;
FIG. 3 is a sequence chart roughly illustrating the second half of the communication procedure carried out in the communication system CS in FIG. 1;
FIGS. 4a to 4d are diagrams each showing a frame format of each packet exchanged in the communication system CS in FIG. 1;
FIG. 5 is a main flowchart illustrating the procedure carried out by a receiving station 1R;
FIG. 6 is a detailed flowchart illustrating the procedure for a reservation phase on the receiving station 1R side;
FIG. 7 is a detailed flowchart illustrating a data communication phase on the receiving station 1R side;
FIG. 8 is a main flowchart illustrating the procedure carried out by a transmitting station 1T;
FIG. 9 is a detailed flowchart illustrating the procedure for a reservation phase on the transmitting station 1T side;
FIG. 10 is a detailed flowchart illustrating a data communication phase on the transmitting station 1T side;
FIGS. 11a to 11c are diagrams each showing information to be registered in a storage device 13R of the receiving station 1R;
FIGS. 12a and 12b are diagrams for each illustrating how to disassemble a communication reservation packet 103 and a data packet 104;
FIG. 13 is the first half of a sequence chart exemplarily illustrating how data is transmitted from the transmitting station 1T to the receiving station 1R;
FIG. 14 is the second half of a sequence chart exemplarily illustrating how data is transmitted from the transmitting station 1T to the receiving station 1R;
FIG. 15 is a sequence chart illustrating how data is exchanged between the transmitting station 1T and the receiving station 1R; and
FIG. 16 is a diagram for illustrating a communication system to which SRMA is applied.



DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a block diagram showing the entire structure of a communication system CS according to an embodiment of the present invention. In the communication system CS, a plurality of communication stations 1 (in the drawing, communication stations 1a, 1b, and 1c are shown) are communicably connected through a wireless transmission path 2.
The communication stations 1 are provided, in advance, with each different identifier ID, thereby being uniquely identified in the communication system CS. In this embodiment, the communication stations 1a to 1c are each provided with the identifiers ID“a” to ID“c”.
Once such communication system CS is started, data is transmitted between the communication stations 1. Hereinafter, any communication station 1 which transmits the data is referred to as a transmitting station 1T, and any other communication station 1 which receives the data is as a receiving station 1R. In the communication system CS, the receiving stations 1R reserves bandwidths used in data communication for the transmitting stations 1T in advance. Hereinafter, a communication procedure for bandwidth reservation is referred to as a reservation phase, and a procedure for data communication a data communication phase.
A typical example for the communication procedure between the receiving stations 1R and the transmitting stations 1T is described by referring to sequence charts in FIGS. 2 and 3. Herein, it is described a case where the communication station 1a operates as the receiving station 1R, and the communication stations 1b and 1c each operate as the transmitting station 1T.
In the reservation phase, the receiving station 1, assembles a request inquiry packet 101 so as to make an inquiry about whether any communication station 1 in the communication system CS (except the receiving station 1R) is requesting for data communication. More specifically, the receiving station 1R assembles, as shown in FIG. 4a, the request inquiry packet 101 from a source identifier SID which is the identifier ID assigned thereto, a packet type T, a unique word UW, and a frame check sequence FCS in addition to a transmission probability value P.
The unique word UW is typically the information necessary for the communication stations 1 receiving the request inquiry packet 101 to establish frame synchronization or to identify the bit position of other information subsequent thereto (e.g., packet type T).
The packet type T is the information necessary for the communication stations 1 to identify the received packet as the request inquiry packet 101.
To the source identifier SID, the identifier ID assigned to the receiving station 1R which assembles the request inquiry packet 101 is set.
The transmission probability value P is later described, and is not now described.
The frame check sequence FCS is the code for the communication stations 1 receiving the request inquiry packet 101 to judge whether any errori is occurred in the request inquiry packet 101, or to correct any error occurred therein.
The receiving station 1R sends out such request inquiry packet 101 to the wireless transmission path 2 so as to make an inquiry about whether any other communication station 1 is requesting for data communication (sequence Seq 11).
Among the communication stations 1, any station having data to be transmitted to the receiving station 1R (the transmitting station 1t) receives the request inquiry packet 101 through the transmission path 2 for disassembly. The transmitting station 1T then assembles a reservation request packet 102 for requesting data communication with the receiving station 1R, and bandwidth reservationnecessaryforthedatacommunication. Inmoredetail, the transmitting station 1T assembles, as shown in FIG. 4b, the reservation request packet 102 from a destination identifier DID, the source identifier SID, the packet type T, the unique word UW, and the frame check sequence FCS in addition to a transfer rate R, which is required for the data communication.
The unique word UW is typically the information necessary for the communication stations 1 receiving the reservation request packet 102 (the receiving station 1R) to establish frame synchronization or to identify the location of other information subsequent thereto (e.g., packet type T).
The packet type T is the information for identifying the reservation request packet 102. The packet type T accordingly enables the receiving station 1R to identify the received packet as the reservation request packet 102.
To the source identifier SID, the identifier ID of the transmitting station 1T which assembles the reservation request packet 102 is set.
To the destination identifier DID, the identifier ID of the receiving station 1R which receives the reservation request packet 102 is set.
The transfer rate R is the information indicating the transfer rate necessary for data communication (i.e., bandwidth).
The frame check sequence FCS is the code for the communication stations 1 receiving the reservation request packet 102 to judge whether any error is occurred in the reservation request packet 102, or to correct any error occurred therein.
The communication station 1b, which is one of the transmitting stations 1T, transmits such reservation request packet 102 to the receiving station 1R through the wireless transmission path 2 for requesting data communication and bandwidth reservation therefor (sequence Seq21).
The receiving station 1R repeats the assembly and transmission of the request inquiry packet 101 for M times (where M is a variable, and is an integer equal to or more than 0) (sequence Seq11 to 1M) so as to collect requests for data communication from some more transmitting stations 1T. In this example, the receiving station 1R presumably assembles and transmits M pieces of request inquiry packets 101 and receives requests for data communication from the communication stations 1b and 1c.
After such collection, the receiving station 1R reserves, for each of the requesting transmitting stations 1T, a bandwidth necessary for data communication so as to determine how many communication reservation packets 103 are to be transmitted in total N (where N is a variable, and is an integer equal to or more than 0). Herein, the number N is determined in relation to the bandwidths necessitated by the transmitting stations 1T for data communication. Immediately after the startup of the communication system CS, the number N is preferably a value which ensures the transfer rate R required by each transmitting station 1T which transmitted the reservation request packet 102. Note that, since each transmitting station 1T can freely request the requiring transfer rate R to the receiving station 1R, the determined number N may be not always ensure the transfer rate R desired by every transmitting station 1T. One of the features of the present invention is to generate information referred to as valid period VP for every transmitting station 1, after the receiving station 1R reserved a bandwidth therefor. The valid period VP is the value denoting how long each bandwidth reserved for the transmitting stations 1T is valid, and an initial value thereof is VP0. In this example, valid periods VPb and VPc whose initial values are each VP0b and VP0c are presumably generated for the communication stations 1b and 1c, respectively (see arrow A in FIG. 2).
After such reservation phase, the data communication phase follows. Therein, the receiving station 1R assembles one communication reservation packet 103 to inform each transmitting station l1 of the bandwidth reserved therefor. To be more specific, the receiving station 1R assembles, as shown in FIG. 4c, the communication reservation packet 103 from the packet type T, the unique word UW, and the frame check sequence FCS in addition to the valid period VP.
Herein, the communication reservation packet 103 does not include the source identifier SID and the destination identifier DID for the purpose of making the packet length shorter. Without being included therewith, the communication reservation packet 103 is correctly received by the targeted transmitting station 1T. As to a manner how to assemble the communication reservation packet 103, it is later described in step S63 in FIG. 7 and is not now described.
The unique word UW is typically the information necessary for the communication stations 1 receiving the communication reservation packet 103 (the transmitting stations 1T) to identify the location of other information subsequent thereto (e.g., packet type T).
The packet type T is the information for identifying the communication reservation packet 103. The packet type T accordingly enables the transmitting stations 1, to identify the received packet as the communication reservation packet 103.
The communication reservation packet 103 is provided with the valid period VP. Accordingly, the transmitting stations it are each informed of the value of the valid period VP updated on the receiving station 1R side, and can judge the validity thereof.
The frame check sequence FCS is the code for the communication stations 1 receiving the communication reservation packet 103 to judge whether any error is occurred in the communication reservation packet 103, or to correct any error occurred therein.
Such communication reservation packet 103 is sent out to the wireless transmission path 2 by the receiving station 1R, and is then received by the targeted transmitting station 1T for disassembly (sequence Seq31). In this example, the communication reservation packet 103 is presumably transmitted to the transmitting station 1b.
The transmitting station 1T divides data for transmission, according to a predetermined size, into several data blocks DB. After receiving the communication reservation packet 103, the transmitting station 1T assembles a data packet 104 so as to transmit one of the data blocks DB to the receiving station 1R. In more detail, the transmitting station 1T assembles, as shown in FIG. 4d, the data packet 104 from the packet type T, the unique word UW, and the frame check sequence FCS in addition to the data block DB.
The unique word UW is typically the information necessary for the communication stations 1 receiving the data packet 104 (the receiving station 1R) to identify the location of other information subsequent thereto (e.g., packet type T).
The packet type T is the information for identifying the data packet 104, and accordingly enables the receiving station 1R to identify the received packet as the data packet 104.
The frame check sequence FCS is the code for the communication stations 1 receiving the data packet 104 to judge whether any error occurred in the data packet 104, or to correct any error occurred therein.
Herein, the data packet 104 is not provided with the source identifier SID and the destination identifier DID similarly to the communication reservation packet 103. Without being included therewith, the data packet 104 is correctly received by the targeted receiving station 1R As to a manner how to assemble the data packet 104, it is later described in step S143 in FIG. 10 and is not now described.
Such data packet 104 is sent out to the wireless transmission path 2 by the transmitting station 1T, and is received by the receiving station 1R for disassembly (sequence Seq41). In this example, the data packet 104 is presumably sent out by the communication station 1b.
The receiving station 1R repeats the transmission of the communication reservation packet 103 for N times (sequence Seq31 to 3N) so as to receive the data packets 104 from the transmitting stations 1T for disassembly. The receiving station 1R then updates, in a manner corresponding to a status for receiving of each data packet 104, the valid period VP each provided to the transmitting stations 1T which transmitted the data packets 104. More specifically, if the receiving station 1R received no data packet 104 from some transmitting station 1, which was supposed to transmit the packet, the valid period provided thereto is shortened. If the receiving station 1R received the data packet 104 from some transmitting station 1T, the valid period provided thereto is lengthened.
Assuming that the communication station 1b transmits the data packet 104 to the receiving station 1, in response to the communication reservation packet 103 transmitted thereto in sequence Seq31 (sequence Seq41), the receiving station 1R lengthens the valid period VPb of the communication station 1b (see arrow B in FIG. 2).
It is also assumed that the communication reservation packet 103 is transmitted to the communication station 1c in sequence Seq32, however, the receiving station 1R does not receive the data packet 104 therefrom for some reasons. If this is the case, the receiving station 1R shortens the valid period VPC of the communication station 1C (see arrow C in FIG. 2).
In such manner, the data communication phase is through. Hereinafter, as shown in FIG. 2, both the reservation phase and the data communication phase are collectively referred to as a unit packet frame PF.
The communication procedure for the receiving station 1R and the transmitting stations 1T after such first unit packet frame PF1 is shown in FIG. 3. In FIG. 3, another reservation phase follows the first data communication phase, and the receiving station 1R determines how many request inquiry packets 101 are to be transmitted in total M. Thereafter, the receiving station 1R repeats the assembly and sending, to the transmission path 2, of the request inquiry packet 101 (sequences Seq51 to Seq5M) so as to again collect requests for data communication from the transmitting stations 1T. Thereafter, the receiving station 1R reserves any bandwidth necessary for data communication for both the transmitting stations 1T which newly transmitted the reservation request packets 102 this time and the transmitting stations 1T to which the valid period VP has been each set so as to determine how many communication reservation packets 103 are to be transmitted in total N. Unlike the case for immediately after the startup of the communication system CS, the number N herein is preferably a value which ensures the transfer rate R required by both the transmitting stations 1T which newly transmitted the reservation request packets 102 this time and the transmitting stations 1T to which the valid period VP has been each set.
Furthermore, the receiving station 1R generates information referred to as valid period VP for the transmitting stations 1T which newly transmitted requests in this reservation phase (see arrow D in FIG. 3).
Hereinafter, in a similar manner to the above, data communication is performed between the receiving station 1R and the transmitting stations 1T by exchanging the communication reservation packets 103 and the data packets 104 therebetween. In the communication system CS, the unit packet frame PF being the combination of the reservation phase and the data communication phase is repeated.
As is described in the foregoing, the valid period VP is lengthened or shortened. Therefore, if a certain transmitting station 1T does not transmit the data packet 104 for some time, the validperiodVP thereof becomes invalid in due time (that means, VP becomes equal to a given reference value VPREF). When the valid period VP provided to some transmitting station 1T becomes equal to the reference value VPREF, the receiving station 1R releases a bandwidth reserved for the transmitting station 1T, and stops assembling the communication reservation packet 103 therefor in the following data communication phase (see arrow E in FIG. 3). In other words, the receiving station 1R voluntarily keeps assembling the communication reservation packet 103 for transmission to the transmitting station 1T until the valid period provided thereto becomes equal to the reference value VPREF.
In the example in FIG. 3, the communication station 1c receives the communication reservation packet 103 from the receiving station 1R (see sequence Seq62) but does not transmit the data packet 104. Therefore, in the course of time, the valid period VP thereof becomes equal to the reference value VPREF (see arrow E), consequently the receiving station 1R stops transmitting the communication reservation packet 103 thereto (see the third packet frame PF, for example).
The typical communication procedure in the communication system CS has been described. Note that, as shown in FIG. 1, each communication station 1 is typically structured by a communication controller 11R a counter 12, a storage device 13, a transmitter 14, and a receiver 15 for implementation of such communication procedure. Note that, forconvenience, FIG. 1 only shows the communication stations 1, and 1b by internal structure thereof.
Hereinafter, for the purpose of structurally distinguishing between the receiving station 1R and the transmitting station 1T, each constituent of the receiving station 1R is provided with a small “R” next to the reference numeral thereof. For example, the communication controller 11 provided in the receiving station 1R is denoted by 11R. On the other hand, each constituent of the transmitting station 1T is provided with a small “T” next to the reference numeral thereof. For example, the storage device 13 provided in the transmitting station 1, is denoted by 13T.
First, by referring to FIG. 5, the processing carried out by the receiving station 1R is described in detail. The communication controller 11R sets the transmission probability value P (where P satisfies 0≦P≦1) to an initial value P0 (step S1). The initial value P0 is set in accordance with the design specifications of the communication system CS. As to the transmission probability value P, it is later described by referring to steps S134 and S135 in FIG. 9, and is not now described.
Next, the communication controller 11R sets the number M, which indicates how many request inquiry packets 101 are to be transmitted, to an initial value M0 (step S2). The initial value M0 is set in accordance with the design specifications of the communication system CS.
Thereafter, the communication controller 11R goes to the reservation phase (step S3) FIG. 6 is a detailed flowchart illustrating step S3. In FIG. 6, the communication controller 11R assembles one request inquiry packet 101 from the source identifier SID (that is, the identifier ID assigned to the receiving station 1R), the packet type T, the unique word UW, and the frame check sequence FCS in addition to the current transmission probability value P. The request inquiry packet 101 (see FIG. 4a) is sent out to the wireless transmission path 2 via the transmitter 14R (step S31).
Next, the communication controller 11R judges whether any signal (any one of the packets 101 to 104) has arrived from the wireless transmission path 2 via the receiver 15R (step S32). If no signal has arrived, the procedure goes to later-described step S38. If yes, the communication controller 11R judges whether the unique word UW included in the received signal can be detected. This tells whether any communication collision has currently occurred on the wireless transmission path 2 (step S33).
If the unique word UW is defective and thus cannot be detected, the communication controller 11R judges that some communication collision has currently occurred on the wireless transmission path 2, and thus the procedure goes to later-described step S37. If the unique word UW is detected in step S33, the communication controller 11R judges that no communication collision has currently occurred on the wireless transmission path 2. The procedure thus goes to step S34 so that the communication controller 11R disassembles the received packet.
In step S34 (packet disassembly processing), the communication controller 11R judges whether the received signal is the reservation request packet 102 addressed to the receiving station 1R. To be more specific, the communication controller 11R extracts the packet type T on the basis of the detected unique word UW. When the packet type T indicates the reservation request packet 102 (see FIG. 4b), the communication controller 11R then extracts the destination identifier DID so as to judge whether the DID is the one provided to the receiving station 1R.
When received the reservation request packet 102 addressed to the receiving station 1R, the communication controller 11R extracts the transfer rate R and the source identifier SID therefrom. Further, the communication controller 11R generates the valid period VP whose initial value is VP0. The communication controller 11R then registers, as shown in FIG. 11a, the transfer rate R, the identifier SID, and the valid period VP in the storage device 13R as a set (step S35), and the procedure goes to step S36.
In the communication system CS, other communication stations 1 may be also in the middle of data communication at the same time. It means, in step S34, the communication controller 11R may extract wrong identifier ID assigned to those other communication stations 1. Furthermore, even if the communication controller 11R successfully extracts correct identifier ID in step S34, the packet type T may not indicate the reservation request packet 102. If this is the case, the communication controller 11R discards the received signal, and the procedure goes to step S36.
In a case where step S34 is carried out, it means any one of the packets 101 to 104 is correctly received by the communication controller 11R. This tells that the wireless transmission path 2 is in a state where a probability of communication collision is relatively low. Therefore, the communication controller 11R adds a given value ΔP1 (where Δp1 satisfies 0<ΔP1<1) to the current transmission probability value P (step S36). In this manner, the transmission probability value P set to another request inquiry packet 101 assembled in the next reservation phase is larger.
Step S33 is referred to again. When the communication controller 11R cannot detect the unique word UW, it tells that the wireless transmission path 2 is in a state where the probability of communication collision is relatively high. If this is the case, the communication controller 11R deducts a given value ΔP2 (where Δp2 satisfies ΔP2<1, or ΔP1=ΔP2) from the current transmission probability value P (step S37). In this manner, the transmission probability value P set to another request inquiry packet 101 assembled in the next reservation phase is smaller.
Step S32 is referred to again. When the communication controller 11R could not detect any signal arrived from the wireless transmission path 2, the communication controller 11R judges whether or not a predetermined time TPRE1 has elapsed since the request inquiry packet 101 was transmitted (step S38).
The time TPRE1 is assumptive that the reservation request packet 102 addressed to the receiving station 1R would have reached there by the time. More specifically, the time TPRE1 is a sum of time required for the request inquiry packet 101 to be transferred from the receiving station 1R to the transmitting stations 1T, time required for the transmitting stations 1T to send out the reservation request packets 102 to the wireless transmission path 2 after each received the request inquiry packet 101, time required for the reservation request packet 102 to be transferred from the transmitting stations 1T to the receiving station 1R, and a time margin.
If the time TPRE1 is not passed yet in step S38, the reservation request packet 102 addressed to the receiving station 1R is yet likely to be transmitted. Thus, the procedure returns to step S32 so that the communication controller 11R waits for any signal to be arrived from the wireless transmission path 2.
If the time TPRE1 has been passed, the communication controller 11R judges that the reservation request packet 102 addressed to the receiving station 1R is unlikely to be transmitted, and thus the procedure goes to step S36. If this is the case, it also means that no signal has transferred onto the wireless transmission path 2 for the duration of time TPRE1, and thus the wireless transmission path 2 is in a state where the probability of communication collision is relatively low. Therefore, the communication controller 11R adds a given value ΔP1 (where ΔP1 satisfies ΔP1≦1) to the current transmission probability value P (step S36).
After step S36 or S37, the communication controller 11R is now through with the reservation phase (step S3) in FIG. 5, and next judges whether M pieces of request inquiry packets 101 have been transmitted (step S4). In step S4 for the first reservation phase, it is judged whether the M0 piece(s) of request inquiry packet 101 is transmitted.
If M pieces of request inquiry packets 101 are not transmitted yet, the communication controller 11R goes to the reservation phase in step S3 again so as to send out a new request inquiry packet 101 to the wireless transmission path 2. If the M pieces of request inquiry packets 101 have been transmitted, the procedure goes to step S5.
By the time the procedure reaches step S5, the communication controller 11R may have received one or more reservation request packets 102 from the transmitting stations 1T, and as shown in FIG. 11b, may have registered the transfer rate R, the identifier ID, and the valid period VP in the storage device 13R as a set for every transmitting station 1T The communication controller 11R defines a transmission frequency TF for every registered transmitting station 1T (step S5). More specifically, the transmission frequency TF is a value indicating how many communication reservation packets 103 are to be transmitted for one transmitting station 1T within one unit packet frame PF. Accordingly, the sum of the transmission frequency TF defined for every transmitting station 1T is equal to the number N shown in FIG. 2. The transmission frequency TF for every transmitting station 1T is also registered in the storage device 13R as shown in FIG. 11c. 
Next, the communication controller 11R goes to the data communication phase for processing (step S6). FIG. 7 is a detailed flowchart illustrating step S6.
In FIG. 7, the communication controller 11R first selects one identifier ID from the storage device 13R (see FIG. 11a, 11b, or 11c) (step S61). In this manner, the communication controller 11R selects the destination of the packet in this processing.
Second, the communication controller 11R decides if there is data for transmission to the selected transmitting station 1T (step S62). The judgement in step S62 is dependent on if the communication controller 11R has received, exemplarily from an application in the upper layer, any data for transmission to the transmitting station 1T selected in step S61.
If the communication controller 11R has no data for transmission to the selected transmitting station 1T, the procedure goes to step S63. If any, the procedure goes to later-described step S610.
In step S63, the communication controller 11R retrieves, from the storage device 13R, the identifier ID selected in step S61 and the valid period VP found in the same set as the ID. The identifier ID of the transmitting station 1, is used as the destination identifier DID for the communication reservation packet 103 to be transmitted in this processing. The communication controller 11R also obtains the identifier ID of the receiving station 1R and the packet type T indicating the communication reservation packet 103. The identifier ID of the receiving station 1R is used as the source identifier SID for the communication reservation packet 103 to be transmitted in this processing.
The communication controller 11R calculates a first CRC (Cyclic Redundancy Check) value according to the packet type T, the source identifier SID, the destination identifier DID, and the valid period VP. The first CRC value is obtained from a given generation polynomial as a function of the details of the packet type T, the source identifier SID, the destination identifier DID, and the valid period VP The first CRC value is used as the frame check sequence to be set to the communication reservation packet 103 to be transmitted in this processing.
The communication controller 11R then assembles the communication reservation packet 103 (see FIG. 4c) from the packet type T, the unique word UW, the newly obtained frame check sequence FCS in addition to the valid period VP. Herein, as is described in the foregoing, the communication reservation packet 103 does not include the source identifier SID and the destination identifier DID therein. The communication reservation packet 103 is sent out to the wireless transmission path 2 via the transmitter 14, (step S63), and is received by the transmitting station 1T.
Next, the communication controller 11R judges whether the data packet 104 (see FIG. 4d) addressed to the receiving station 1R has arrived from the wireless transmission path 2 via the receiver 15R (Step S64). As to the reception operation in step S64, it is later described by referring to step S143 in FIG. 10, and is not now described.
When the data packet 104 addressed to the receiving station 1R is received, the communication controller 11R lengthens the valid period VP found in the same set as the selected identifier ID (Step S65). In this embodiment, in step S65, the communication controller 11R exemplarily decrements the current valid period VP by the given value ΔVP, (where ΔVP1 is an arbitrary number) so as to lengthen the valid period VP.
The communication controller 11R is now through with the data communication phase in FIG. 5 (step 6), and the procedure goes to step S7.
If the data packet 104 addressed to the receiving station 1R is not received in step S64, the communication controller 11R judges whether a predetermined time TPRE2 has elapsed since the communication reservation packet 103 was sent out (step S66).
The time TPRE2 is assumptive that the data packet 104 from the transmitting station 1, which received the communication reservation packet 103 would have reached the receiving station 1R by the time. More specifically, the time TPRE2 is a sum of time required for the communication reservation packet 103 to be transferred from the receiving station 1R to the transmitting station 1T, time required for the transmitting station 1T to send out the data packet 104 to the wireless transmission path 2 after received the communication reservation packet 103, time required for the data packet 104 to be transferred from the transmitting station 1T to the receiving station 1R, and a time margin.
If the time TPRE2 is not passed yet in step S66, the procedure returns to step S64 so that the communication controller llwaits for the data packet 104.
If the given time TPRE2 has been passed, the communication controller 11R can judge that the transmitting station 1T which has received the communication reservation packet 103 did not transmit the data packet 104, and thus shortens the valid period VP found in the same set as the selected identifier ID (Step S67). In this embodiment, in step S67, the communication controller 11R exemplarily increments the current valid period VP by the given value ΔVP2 (where ΔVP2 is an arbitrary number) so as to shorten the valid period VP.
Next, the communication controller 11R compares the shortened valid period VP with the given reference value VPREF (step S66). In this embodiment, the valid period VP is lengthened after decremented by the value ΔVP1, and is shortened after incremented by the value ΔVP2. In such case, the reference value VPREF needs to satisfy VP0 (VPREF.
If the valid period VP is less than the reference value VPREF, the communication controller 11R is through with the data communication phase in FIG. 5 (step S6) so as to keep the bandwidth reserved for the transmitting station 1T. Thus, the procedure goes to step S7.
If the valid period VP is equal to or more than the reference value VPREF, the communication controller 11R deletes, so as to release the bandwidth reserved for the transmitting station 1T, the identifier ID of the transmitting station 1T, and the transfer rate R, the valid period VP, and the transmission frequency TF found in the same set as the identifier ID from the storage device 13R (step S69). The communication controller 11R is now through with step S6, and the procedure goes to step S7.
Herein, step S62 is referred to again. While the receiving station 1R is receiving data from the transmitting station 1T, some data may be generated in the receiving station 1R for transmission to the transmitting station 1T. Accordingly, if the receiving station 1R has any data for transmission to the transmitting station 1T in step S62, the communication controller 11R divides the data into several data blocks DB before the procedure goes to step S610.
Next, the communication controller 11R obtains, for the data packet 104, the packet type T, the identifier ID of the receiving station 1R, and the identifier ID of the transmitting station 1T, and one of the data blocks DB. Herein, the identifier ID of the receiving station 1R and the identifier ID of the transmitting station 1T are respectively used as the source identifier SID and the destination identifier DID of the to-be-assembled data packet 104.
The communication controller 11R calculates a first CRC value for the frame check sequence FCS for the data packet 104 to be assembled. The first CRC value is calculated by substituting the function of the details of the packet type T, the source identifier SID, the destination identifier DID, and the valid period VP to the above described generation polynomial.
Thereafter, the communication controller 11R assembles the data packet 104. Herein, the communication controller 11R assembles such data packet 104 as shown in FIG. 4d from the packet type T, the unique word UW, and the frame check sequence FCS in addition to the data block DB. Note that, the data packet 104 does not include the destination identifier DID and the source identifier SID for the purpose of making the packet length shorter.
The communication controller 11R sends out the assembled data packet 104 to the wireless transmission path 2 via the transmitter 14R (step S610), and the procedure goes to step S64.
After being through with step S6, the communication controller 11R judges whether N pieces of communication reservation packets 103 have been sent out (step S7).
If not yet, the communication controller 11R goes to step S6 again so as to send out a new communication reservation packet 103 to the wireless transmission path 2.
If N piece(s) of communication reservation packets 103 have been sent out, the procedure goes to step S8.
By the time the procedure reaches step S8, one unit packet frame PF (see FIG. 2 or 3) has been through. The communication controller 11R determines how many request inquiry packets 101 are to be transmitted in total M for the next unit packet frame PF (step S8). Although any manner will do to determine the number M, it is preferable to be based on how much bandwidth being left unused. To be specific, preferably, the more bandwidth being left unused, the larger the number M becomes.
After the number M is determined for the next unit packet frame PF, the procedure returns to step S3 so that the communication controller 11R repeats the reservation phase and the data communication phase in the same manner as the above, and receives data from the transmitting stations 1T.
Next, by referring to FIG. 8 for flowchart, the operation of one transmitting station 1T is described in detail. In FIG. 8, the communication controller 11T receives data for transmission to a certain communication station 1 (the receiving station 1R), the transfer rate R necessary for the data transmission, and the identifier ID of the receiving station 1R from an application in an upper layer or an interface (step S11), and the procedure goes to step S12.
Then, the communication controller 11T sets a value C of the counter 12T to an initial value C0 (step S12). The value C of the counter 12T is substantially the same as the valid period VP controlled on the receiving station 1R side.
Further, immediately after step S11 is complete, the receiving station 1R does not yet reserve any bandwidth for the transmitting station 1T. Accordingly, at this point in time, the valid period VP of the transmitting station 1T is regarded as having reached the reference value VPREF and being invalid. By taking this into consideration, the initial value C0 is preferably not less than the reference value VPREF of the valid period VP. More preferably, the initial value C0 is set to be equal to the reference value VPREF.
Thereafter, the communication controller 11T goes to the reservation phase (step S13). FIG. 9 is a detailed flowchart illustrating step S13. In FIG. 9, the communication controller 11T compares the current value C of the counter 12T with an internally-stored reference value CREF (step S131). It is preferable that the reference value CREF being equal to the VPREF on the receiving station side 1R.
When the current value C is less than the reference value CREF, the communication controller 11T regards that the valid period VP of the transmitting station 1T is yet valid, and the procedure skips steps onward (steps S132 to S137) and goes to the data communication phase in step S14.
When the current value C is equal to the reference value CREF or more, the communication controller 11T judges it as being immediately after data for transmission to the receiving station 1R is generated or some bandwidth once assigned to the transmitting station 1T is released by the receiving station 1R, and then starts detecting a no-signal period TPNS (step S132). The no-signal period TPNS is selected according to the design specifications of the communication system CS, and more specifically, indicates time required from a certain request inquiry packet 101 being received by the transmitting station 1T to the next request inquiry packet 101 being transferred thereto, and a time margin.
Thereafter, the communication controller 11T judges whether the request inquiry packet 101 (see FIG. 4a) is transmitted from the receiving station 1R through both the wireless transmission path 2 and the receiver 15T (step S133).
The reception operation in step S133 is described next below. First, when some signal is received from the wireless transmission path 2, the communication controller 11T detects the unique word UW included therein. Then, the communication controller 11T extracts the packet type T subsequent to the unique word UW. If the packet type T indicates the request inquiry packet 101, the communication controller 11T extracts the source identifier SID. When the source identifier SID coincides with the identifier ID of the receiving station 1R obtained in step S11, the communication controller 11T regards the request inquiry packet 101 as being received from the receiving station 1R, and the procedure goes to step S134. When the communication controller 11T regards that the received signal is not the request inquiry packet 101 from the receiving station 1R, the communication controller discards the received signal and the procedure goes to later-described step S137.
In step S134, the communication controller 11T generates a random number RN (where RN satisfies 0<RN≦=1). The communication controller 11T also extracts the transmission probability value P from the received request inquiry packet 101 (step S134).
Then, the communication controller 11T compares the random number RN obtained in step S134 with the transmission probability value P for the judgement whether the random number RN satisfies a given criterion (step S135). Ifsatisfied, the communication controller 11T judges that the transmission of the reservation request packet 102 is permitted, and the procedure goes to step S136. If not satisfied, the procedure returns to step S132 so that the communication controller 11T starts detecting the no-signal period TPNS and then waits for a new request inquiry packet 101.
The judgement operation in step S135 is exemplarily described next below. The transmission probability value P is the probability of the transmission of the reservation request packet 102 in response to the request inquiry packet 101 received by the transmitting station 1T. For example, the transmission probability value P of 0.3 indicates that the transmitting station 1T is allowed to transmit the reservation request packet 102 with a probability of 30%. The random number RN takes any number among 0.1, 0.2 . . . 1. If this is the case, the communication controller 11T compares the generated random number RN with the transmission probability value P so as to judge whether or RN≦P is satisfied. If satisfied, the communication controller 11T regards that the transmission of the reservation request packet 102 is permitted, and the procedure goes to step S136. If not satisfied, the procedure returns to step S132.
In step S136, the communication controller 11T assembles the reservation request packet 102 (see FIG. 4b) from the identifier ID of the receiving station 1R obtained as the destination identifier DID exemplarily in step S11, the identifier ID of the transmitting station 1T as the source identifier SID, the packet type T indicating the reservation request packet 102, the unique word UW, and the frame check sequence FCS in addition to the transfer rate R obtained in step S11, and sends out the packet to the wireless transmission path 2 via the transmitter 14T (step S136). The communication controller 11T is through with the reservation phase in FIG. 8 (step S13), and the procedure goes to step S14.
Note that, the reservation request packet 102 sent out to the wireless transmission path 2 is received by the receiving station 1R. In response thereto, the receiving station 1R goes to the processing described in step S35 in FIG. 6.
Herein, step S133 is referred to again. When the request inquiry packet 101 is not received, the communication controller 11T judges whether the no-signal period TPNS was detected on the wireless transmission path 2 (step S137).
When the no-signal period TPNS is not detected, the communication controller 11T decides that now is the time to transmit the reservation request packet 102, and the procedure goes to step S136. Then, the communication controller 11T assembles the reservation request packet 102 in the same manner as the above for transmission to the receiving station 1R (step S136). The communication controller 11T is through with the reservation phase in FIG. 8 (step S13), and the procedure goes to step S14.
When the no-signal period TPNS is not detected in step S137, the communication controller 11T decides that now is not the time to transmit the reservation request packet 102. In this case, the procedure returns to step S132 so that the communication controller 11T starts detecting the no-signal period TPNS and waits for a new request inquiry packet 101.
The communication controller 11T then goes to the data communication phase after being through the reservation phase (step S13 in FIG. 8) (step S14). FIG. 10 is a detailed flowchart illustrating step S14. In FIG. 10, the communication controller 11T judges whether or not the communication reservation packet 103 (see FIG. 4c) addressed to the transmitting station 1T is transmitted from the receiving station 1R through the wireless transmission path 2 and the receiver 15T (step S141).
As being peculiar to the present invention, the reception operation in step S141 is described by referring to FIG. 12a. After detected an incoming signal from the wireless transmission path 2, the communication controller 11T detects the unique word UW included therein. The communication controller 11T then extracts the packet type T subsequent to the unique word UW (see arrow A).
When the packet type T indicates the communication reservation packet 103, the communication controller 11T extracts the valid period VP from the received communication reservation packet 103 (see arrow B). The communication controller 11T also retrieves the identifier ID of the receiving station 1R obtained exemplarily in step S11 and the previously-stored identifier ID of the transmitting station 1T (See arrows C and D). The communication controller 11T substitutes the packet type T, the identifier ID of the receiving station 1R, and the identifier ID of the transmitting station 1T, and the valid period VP to the above-described generation polynomial so as to calculate a second CRC value for judgement (see arrow E)
As is described in step S63, the frame check sequence FCS of the communication reservation packet 103, i.e., the first CRC value is calculated from the packet type T, the source identifier SID (i.e., identifier ID of the receiving station 1R), the destination identifier DID (i.e., identifier ID of the transmitting station 1T), and the valid period VP. Accordingly, assuming that the transmitting station 1T is the correct destination of the communication reservation packet 103, the second CRC value coincides with the first CRC value of the communication reservation packet 103. If the values agree with each other, the communication controller 11T regards that the received communication reservation packet 103 is the one addressed to the transmitting station 1T, and no error is detected therein.
When the communication controller 11T could not receive the communication reservation packet 103 addressed to the transmitting station 1T in step S141, the procedure goes to later-described step S146. On the other hand, when received, the communication controller 11T so updates the value C of the counter 12T that the valid period VP controlled in the receiving station 1R coincides therewith (step S142). In this manner, the value C of the counter 12T is synchronized with the valid period VP.
Next, the communication controller 11T obtains, for the data packet 104, the packet type T, the identifier ID of the transmitting station 1T, the identifier ID of the receiving station 1R, and one data block DB. Herein, the identifier ID of the transmitting station 1T and the identifier ID of the receiving station 1R are respectively used as the source identifier SID and the destination identifier DID for the data packet 104 to be assembled.
The communication controller 11T calculates the first CRC value for the data packet 104 to be assembled as the frame check sequence FCS. The first CRC value is calculated by substituting, to the above-described generation polynomial, the function of the details of the data packet T, the source identifier SID, the destination identifier DID, and the data block DB.
Thereafter, the communication controller 11T assembles the data packet 104. Herein, the communication controller 11T assembles such data packet 104 as shown in FIG. 4d from the packet type T, the unique word UW, and the frame check sequence FCS in addition to the data block DB. Note that, the data packet 104 does not include the source identifier SID and the destination identifier DID for the purpose of making the packet length shorter.
The communication controller 11T sends out the assembled data packet 104 to the wireless transmission path 2 via the transmitter 14T (step S143). After receiving the data packet 104, the receiving station 1R goes to the processing in step S64 in FIG. 7 so as to receive and disassemble the data packet 104.
Step S64 for the receiving station 1R is now described by referring to FIG. 12b. The communication controller 11R detects the unique word UW included in an incoming signal from the wireless transmission path 2, and then extracts the packet type T subsequent thereto (see arrow A).
When the packet type T indicates the data packet 104, the communication controller 11R extracts the data block DB therefrom (see arrow B). The communication controller 11R also extracts the identifier ID of the transmitting station 1T obtained exemplarily in step S35, and the previously-stored identifier ID of the receiving station 1R (see arrows C and D). The communication controller 11R substitutes, to the above-described generation polynomial, the packet type T, the identifier ID of the transmitting station 1T, the identifier ID of the receiving station 1R, and the data block DB so as to calculate the second CRC value for judgement (see arrow E).
The frame check sequence FCS of the data packet 104, i.e., the first CRC value is calculated, as described in step S143, from the packet type T, the source identifier SID (i.e., identifier ID of the transmitting station 1T), the destination identifier DID (i.e., identifier ID of the receiving station 1R), and the data block DB. Accordingly, assuming that the receiving station R is the correct destination of the data packet 104, the calculated second CRC value coincides with the first CRC value of the data packet 104. When the values agree with each other, the communication controller 11R regards that the received data packet 104 is the one addressed to the receiving station 1R and no error is detected therein, and the procedure goes to step S65 in FIG. 7. When the values do not agree with each other, the procedure goes to step S66.
FIG. 10 is referred to again. Since the transmitting station 1T has transmitted the data packet 104 in step S143, the valid period VP assigned thereto is lengthened on the receiving station 1R side. Accordingly, after step S143 is through, the communication controller 11T updates the current value C of the counter 12T (step S144). Since the receiving station 1, lengthens the valid period VP by (VP−ΔVP) in this embodiment, the communication controller 11T decrements the current value C of the counter 12T by a given value ΔC. Herein, in order to synchronize between the value C of the transmitting station 1T and the valid period VP of the receiving station 1R, it is preferable that the value ΔC is equal to the value ΔVP.
Next, the communication controller 11T judges whether the current value C of the counter 12T is equal to a reference value CREF or more (step S145).
If the value C is less than reference value CREF, the communication controller 11T regards that the valid period of the transmitting station 1T is still valid, and the procedure returns to S141 so that the communication controller 11T keeps going through the data communication phase.
If the value C is not less than the reference value CREF in step S145, it is useless for the communication controller 11T going through the data communication phase. Thus, the communication controller 11T is through with the data communication phase in FIG. 10 (step S14), and the procedure goes to step S15 in FIG. 8.
Step S 141 in FIG. 10 is referred to again. Immediately after the communication controller 11T judged that the received signal is not the communication reservation packet 103 addressed to the transmitting station 1T, the procedure goes to step S146. Thereafter, the communication controller 11T judges whether the data packet 104 (transmitted in step S610) addressed to the transmitting station 1T has arrived (step S146). Since the reception operation in step S146 is similar to step S64 in FIG. 7 (see FIG. 12b), it is not described again.
In a case where the data packet 104 arrives the communication controller 11T in step S146, the procedure goes through steps S143 and S144 before the communication controller 11T being through with the data communication phase in FIG. 10 (step S14), and then the procedure goes to step S15 in FIG. 8.
On the other hand, when the data packet 104 is not received, the communication controller 11T judges whether a predetermined time TPRE2 has elapsed since the reservation request packet 102 was transmitted in step S136 (step S147).
The time TPRE3 is assumptive that the communication reservation packet 103 from the receiving station 1R would have reached the transmitting station 1T by the time. More specifically, the time TPRE3 is a sum of time required for the reservation request packet 102 to be transferred from the transmitting station 1T to the receiving station 1R, time required for the receiving station 1R to send out the communication reservation packet 103 to the wireless transmission path 2 after received the reservation request packet 102, time required for the communication reservation packet 103 to be transferred from the receiving station 1R to the transmitting station 1T, and a time margin.
If the predetermined time TPRE3 is not passed yet, the procedure returns to step S141 so that the communication controller 11T waits for the communication reservation packet 103 addressed to the transmitting station 1T.
If the predetermined time TPR3 has been passed, the communication controller 11R can regard that the communication reservation packet 103 which was supposed to be transmitted from the receiving station 1R did not arrive. If this is the case, it is assumable that the receiving station 1R shortens the valid period VP of the transmitting station 1T, thus the procedure goes to step S148 so that the communication controller 11T updates the current value C of the counter 12, (step S148). In this embodiment, the receiving station 1R shortens the valid period VP by (VP+ΔVP). Therefore, the communication controller 11T increments the current value C of the counter 12T by the value ΔC.
After step S148 is thorough, the communication controller 11T is through with the data communication phase in FIG. 10 (step S14), and the procedure goes to step S15 in FIG. 8.
In step S15, the communication controller 11T judges whether any data block DB is left for transmission to the receiving station 1R (step S15). When there is any data block DB being left, the procedure returns to step S13 for the processing in FIG. 9 again. If not, the procedure returns to step S11 so that the communication controller 11T waits for new data, for example.
The procedure for both the receiving stations 1R and the transmitting stations 1T is now thoroughly described in a specific manner. With the procedure, such communication shown in the sequence charts in FIGS. 13 and 14 is carried out between the receiving stations 1R and the transmitting stations 1T. It is assumed next below that the communication station 1a operates as the receiving station 1R, and the communication station 1b operates as the transmitting station 1T.
First, the communication station 1a goes through steps S1 and S2 in FIG. 5. For convenience, the initial value P0 of the transmission probability value P is “0.3”, and the initial value M0 of the transmission number M is “2”. Next, the communication station 1a assembles one request inquiry packet 101 (see FIG. 4a) (FIG. 6; step S31). The request inquiry packet 101 includes the identifier ID “a” as the source identifier SID and the transmission probability value P of “0.3”, and is sent out to the transmission path 2 (sequence Seq111). Then, the communication station 1a waits for the reservation request packet 102 addressed thereto from the communication stations 1 (except the communication station 1).
At the time of sequence Seq111, the communication station 1b is through with steps S11 and S12 in FIG. 8, obtained the identifier ID“a” of the receiving station 1R from an application in an upper layer etc., and set the initial value C0 of the counter 12b to “3”.
After step S12 is through, the procedure goes to steps S131 and S132 in FIG. 9. Herein, the reference value CREF is assumed to be “3”.
The communication station 1b then receives the request inquiry packet 101 transmitted in sequence Seq111 (step S133), and generates the random number RN (step S134). Assuming that the generated random number RN is “0.4”, the communication station 1b decides that “RN≦P” is not satisfied since the transmission probability value P of the received request inquiry packet 101 is “0.3” (step S135, see arrow A in FIG. 13). Thus, the procedure returns to step S132, and the communication station 1b waits for a new request inquiry packet 101.
As is described in the foregoing, the communication station 1b does not transmit the reservation request packet 102. Assuming that none of other communication stations 1 responded to the request inquiry packet 101 transmitted in sequence Seq111 the communication station 1a repeats the processing in steps S32 to S38 until the predetermined time TPRE1 is passed. The procedure then goes to step S36. If this is the case, the communication station 1a presumably determines that the wireless transmission path 2 is not congested and increases the transmission probability value P to “0.4” (step S36).
Since the transmission number M is “2” and so far one request inquiry packet 101 has been transmitted, the procedure returns to step S3 after step S4 in FIG. 5.
The communication station 1a then assembles one request inquiry packet 101 (step S31 in FIG. 6). The request inquiry packet 101 is provided with the transmission probability value P of “0.4”, and is sent out to the wireless transmission path 2 (sequence Seq112). Thereafter, the communication station 1a waits for the reservation request packet 102 addressed thereto.
During sequences Seq112, and Seq112, a loop which consists of steps S132, S133 and S137 is repeated. At this time, the communication station 1b receives the request inquiry packet 101 transmitted in sequence Seqll2 after received the request inquiry packet 101 transmitted in sequence Seq112, but before detecting the no-signal period TPNS. Therefore, the procedure goes to step S134, and the communication station 1b generates the random number RN. The random number RN herein is presumed to be “0.2”. If this is the case, the communication station 1b determines that “RN≦P” is satisfied in step S135 since the current transmission probability value P is “0.4” (see arrow B in FIG. 13).
The procedure then goes to step S136 so that the communication station 1b assembles one reservation request packet 102 (see FIG. 4b), sends out the packet to the communication station 1a (sequence Seq121), and waits for the communication reservation packet 103 therefrom.
Although a loop which consists of steps S32 and S38 is repeated, the communication station lamay receive the reservation request packet 102 transmitted in sequence Seq121 before the predetermined time TPRE1 is passed. Thus, the procedure goes to step S33 after step S32 is through. Assuming that currently no communication collision has occurred, the communication station 1a disassembles the received packet in step S34 and regards that the reservation request packet 102 addressed has arrived. Thereafter, the communication station 1a registers the transfer rate R, “b” as the source identification SID, and the initial value VPO of the valid period VPb, which are extracted from the received reservation request packet 102, in the storage device 13a as a set. Herein, the initial value VP0 is assumed to be “3”.
Thereafter, the transmission probability value P is increased (step S36). Then, since two request inquiry packets 101 have been transmitted, the procedure goes to step S5 after step S4 is through. At this point in time, the communication station 1a has only received the reservation request packet 102 from the communication station 1b, the transmission frequency TF with respect to the communication station 1b is defined. The transmission frequency TFb is assumed to be “2” (see arrow C in FIG. 13).
Next, the communication station 1a selects “b” for the registered identifier ID, and then assembles the communication reservation packet 103 including the valid period VPb of “3” (steps S61 to S63 in FIG. 7). To the communication reservation packet 103 in this example, the valid period VPb of “3” is set. Further, to the frame check sequence FCS, the above-described first CRC value is set. The communication station 1a sends out the assembled communication reservation packet 103 to the communication station 1b through the wireless transmission path 2 (sequence Seq131), then, waits for the data packet 104 addressed thereto.
After the reservation request packet 102 is sent out in sequence Seq121, the communication station 1b goes to the data communication phase in FIG. 10. Assuming that no signal (except the communication reservation packet 103) has been sent out to the wireless transmission path 2 during sequences Seq 121 and Seq131, the communication station 1b correctly receives the communication reservation packet 103, which is transmitted in sequence Seq131, in step S141 carried out immediately after sequence Seq131. At this time, as is described in the foregoing, the communication station 1b calculates the second CRC value, and determines that the received packet is the communication reservation packet 103 addressed thereto.
Thereafter, the communication station 1b so updates the value C of the counter 12b that the valid period VPb of the communication reservation packet 103 coincides therewith (step S142), and then assembles one datapacket 104 (FIG. 4d) (step S143) Herein, to the frame check sequence FCS, the first CRC value is set. The communication station 1b then transmits the assembled data packet 104 to the communication station 1a through the wireless transmission path 2(sequence Seq141)
Next, the communication station 1b decrements the value C of the counter 12b by ΔC (step S144). If the value ΔC is assumed to be “1” in this example, the value C at this time is “2”. Then, the communication station 1b judges whether the current value C of the counter 12b is equal to the reference value CREF or more (step S145). Since the reference value CREF is “3”, the procedure returns to step S14, so that the communication station 1b waits for a new communication reservation packet 103.
Herein, it is assumed that, after the communication station 1a sent out the communication reservation packet 103 in sequence Seq131, a loop which consists of steps S64 and S66 in FIG. 7 is repeated during sequences Seq131 and Seq141. In such case, instep S64 immediately after sequence Seq141, the communication station 1a receives the data packet 104 addressed thereto which was transmitted in sequence seq141. At this time, as described in the foregoing, the communication station 1a calculates the second CRC value, determines that the received packet is the data packet 104 addressed thereto, and then extracts the data block DB for storage.
Thereafter, the procedure goes to step S65 so that the communication station 1a decrements the valid period VP of the communication station 1b registered in the storage device 13a by ΔVP so as to lengthen the valid period VP. In this example, the value ΔVP is assumed to be “1” being equal to the value ΔC. Accordingly, the valid period VPb of the communication station 1b is currently “2” (see arrow D in FIG. 13).
The communication station 1b is then through with the data communication phase in step S6, and the procedure goes to step S7. Since the communication station 1, does not yet transmit the communication reservation packet 103 for the required number of pieces, the procedure returns to step S6 for the data communication phase (see FIG. 7) again.
After selected “b” for the registered identifier ID, the communication station 1a assembles the communication reservation packet 103 including the valid period VPb of “2” in the same manner as above (steps S61 to S63). The communication station 1a then transmits the assembled communication reservation packet 103 to the communication station 1b through the wireless transmission path 2 (sequence Seq132), and waits for the data packet 104 addressed thereto (steps S64 and S66).
After sent out the data packet 104 in sequence Seq141, the communication station 1b goes to the reservation phase in FIG. 9. Since, at this time, the value C of the counter 12b is “2” and the reference value CREF is “3”, the communication station 1b skips the reservation phase to the data communication phase in FIG. 10. Assuming that no signal has been sent out to thewireless transmission path 2 during sequences Seq141 and Seq132, a loop which consists of steps S141, 5146 and S147 is repeated. The communication station 1b correctly receives, in step S141 immediately after sequence Seq132, the communication reservation packet 103 transmitted in sequence Seq132.
Then, the procedure goes to step S142 so that the communication station 1b assembles one data packet 104 for transmission to the communication station 1a through the wireless transmission path 2 (step S143, sequence Seq142).
Next, the communication station 1b decrements the value C of the counter 12b by ΔC (step S144) so as to update the value to “1”. If there is any data for transmission is left, the procedure returns to the reservation phase in step S13 after step S15 in FIG. 8 is completed.
Assuming that no signal has been sent out to the wireless transmission path 2 during sequences Seq132 and Seq142, a loop which consists of steps S64 and S66 is repeated. The communication station 1a receives, in step S64 immediately after sequence Seql42, the data packet 104 transmitted in sequence Seql42, and extracts the data block DB for storage.
The communication station 1a then decrements the valid period VP of the communication station 1b by AVP (Step S65) so as to update the value to “1”.
The communication station 1a is through with the data communication phase in step S6, and the procedure goes to step S7. Since the communication station 1a has transmitted the communication reservation packet 103 for the required number of pieces, the procedure goes to step S8 so that the communication station 1a determines the transmission number M for the next unit packet frame. In this example, the transmission number M is presumably determined as “1”.
Such sequence Seq11 to Seq14 forms the first unit packet frame PF1.
The communication station 1 then goes to the reservation phase in step S3, i.e., step S31 in FIG. 6, so as to assemble one request inquiry packet 101 for transmission to the wireless transmission path 2 (sequence Seq151). To the request inquiry packet 101, the transmission probability of “0.5” is set. Then, the communication station 1a waits for the reservation request packet 102 from any communication station 1 having a request for data communication therewith.
For convenience, it is assumed herein that a plurality of communication stations 1 (except the communication station 1b) concurrently transmit the reservation request packets 102 in response to the request inquiry packets 101 transmitted in sequence Seq151, and consequently some communication collision occurs on the wireless transmission path 2 (sequence Seq161)
Herein, although a loop which consists of steps S13 to S15 is repeated in sequence Seq151, the communication station 1b goes to the data communication phase directly from step S131 in the reservation phase. Therefore, the communication station 1b does not receive the request inquiry packet 101.
By referringto FIG. 14 forsequencecart, thecommunication procedure between the communication stations 1a and 1b is described next below.
After sequence Seq151, steps S32 to S38 are repeated. However, since the communication station 1a receives several collided reservation request packets 102 before the predetermined time TPRE1 is passed, the procedure goes to step S37 after step S33. The communication station 1a decreases the transmission probability value P (step S37) to “0.4”. The procedure then returns to step S4 in FIG. 5. Since so far one request inquiry packet 101 has been transmitted, and the current transmission number M is “1”, the procedure then goes to step S5. In this reservation phase, the communication station 1a cannot correctly receive the reservation request packet 102 from the new communication stations 1. Therefore, in step S5, the transmission frequency TFb with respect to the transmitting station 1b is presumably determined as “2” again (see arrow F in FIG. 14).
Then, the procedure goes to steps S61 to S63 in FIG. 7 so that the communication station 1a selects “b” for the registered identifier ID, and assembles the communication reservation packet 103 for transmission to the communication station 1b (sequence Seq171). To the communication reservation packet 103, the valid period VP of “1” is set. Thereafter, the communication station 1a waits for the data packet 104 addressed thereto.
The communication station 1b has been waiting for the communication reservation packet 103 from the communication station 1a after transmitted the data packet 104 in sequence Seq142, and receives the communication reservation packet 103 in step S141 immediately after sequence Seq171.
Next, in step S142, the communication station 1b first equalizes the value C of the counter 12b with the valid period VP of “1”, and in step S143, assembles one data packet 104 for transmission to the communication station 1a through the wireless transmission path 2 (sequence Seq181).
The procedure then goes to step S144 so that the communication station 1b decrements the value C of the counter 12b by ΔC to obtain “0” (see arrow G in FIG. 14). Then, the communication station 1b determines that there is no more data for transmission (data block) left (step S15), and the procedure returns to step S11 in FIG. 8.
Assuming that no signal has been sent out to the wireless transmission path 2 after the communication station 1a transmitted the communication reservation packet 103 in sequence Seq171 but before sequence Seq181. If this is the case, in step S64 immediately after sequence Seq181, the communication station 1a receives the data packet 104 transmitted in sequence Seq18, and then extracts the data block DB therefrom for storage. In this manner, the communication controller 11a of the Communication station 1b may receive every data transmitted from the communication station 1b, thus transmits the data to the application in the upper layer, for example.
The communication station 1 decrements, by AVP, the valid period VPb of the communication station 1b registered in the storage device 13a to obtain “0” (step S65).
Although the procedure goes to step S7 in FIG. 5, since the communication station 1a does not yet transmit the communication reservation packet 103 for the required number of pieces, the procedure returns to step S6 for the data communication phase again.
The communication station 1a selects “b” for the registered identifier ID, and then, in a similar manner to the above, assembles the communication reservation packet 103 including the valid period VPb of “0” (steps S61 to S63). The communication station 1a transmits the assembled communication reservation packet 103 to the communication station 1b through the wireless transmission path 2 (sequence Seq172), then waits for the data packet 104 therefrom.
Since the communication station 1b has already transmitted every data to the communication station 1a, now is waiting for new data to be transmitted from the application of the upper layer etc., and the like (step S11 in FIG. 8). Accordingly, the communication station 1b neglects the communication reservation packet 103 transmitted in sequence Seq172. As a result, steps S64 and S66 are repeated thereafter, but the procedure soon goes to step S67 after S66.
The communication station 1a then increments, by ΔVP, the valid period VPb registered in the storage device 13, to obtain “1” (see arrow H in FIG. 14, step S67).
The communication station 1a then judges whether the valid period VPb is equal to the reference value VPREF or more (step 368). Assuming that the reference value VPREF is previously set to “4”, the communication station 1a is through with the data communication phase in FIG. 5 with the reason that the valid period VPb is “1”, and the procedure goes to step S7.
Since the communication station 1a has already transmitted the communication reservation packet 103 for the required number of pieces, the procedure goes to step S8 so that the communication station 1a determines the transmission number M for the next unit packet frame. In this example, the transmission number M is presumably determined as “1”.
Such sequence Seq15 to Seq18 forms the second unit packet frame PF2.
In the third unit packet frame PF3 and onwards, the communication station 1a operates in the same manner as in the unit packet frame PF2 and transmits the communication reservation packet 103 to the communication station 1b. However, as the communication station 1b has been waiting for new data to be transmitted since sequence Seq181, and thus neglects the communication reservation packet 103 even if the packet is addressed thereto.
Accordingly, every time the communication station 1a transmits the communication reservation packet 103 to the communication station 1b, the communication station 1a goes to step S67 so as to shorten the valid period VP (see arrow I in FIG. 14). Consequently, the valid period VP of the communication station 1b will be soon equalized with the reference value VPREF. When determined that the valid period VP of the communication station 1b is now equal to or more than the reference value VPREF in step S68, the communication station 1a deletes the set of transfer rate Rb, the identifier ID, the valid period VPb, and the transmission frequency TFb from the storage device 13a in step S69. In this manner, the communication station 1a releases the bandwidth reserved for the communication station 1b (see arrow J in FIG. 14).
After the deletion, the communication station 1a does not transmit the communication reservation packet 103 to the communication station 1b unless the communication station 1a receive any new reservation request packet 102 therefrom.
As described in the foregoing, the communication station 1a, operating as the receiving station 1R reserves a bandwidth for the communication station 1b as the transmitting station 1T in response to the reservation request packet 102. In addition, for the purpose of controlling the reserved bandwidth, the communication station 1a registers the identifier ID“b” of the communication station 1b, the transfer rate Rb, the valid period VPb, and the transmission frequency TFb as a set in the storage device 13a. Herein, the valid period VPb is lengthened or shortened depending on the data packet 104 transmitted from the communication station 1T. The communication station 1a voluntarily keeps transmitting, on the basis of the transmission frequency TFb, the communication reservation packet 103 to the communication station 1b as long as the valid period thereof is valid, and reserving the bandwidth therefor.
In this manner, as shown in FIGS. 13 and 14, as long as the valid period VP is valid after the transmission of the reservation request packet 102 to the communication station 1a, the communication station 1b can more swiftly transmit the data packet 104 by responding to the communication reservation packet 103 addressed thereto. As a result, in the communication system CS, the frequency of transmitting the reservation request packet 102 for bandwidth reservation is considerably reduced compared with the SRMA described in the Background Art. Accordingly, the overhead for the bandwidth reservation in this communication system CS is decreased, and thus bandwidths of the wireless transmission path 2 can be more effectively utilized.
Further, when it is assumed that any communication collision occurs on the wireless transmission path 2, the receiving station 1R relatively lowers the transmission probability value P of the request inquiry packet 101. In this manner, even if the transmitting station 1T has any data for transmission to the receiving station 1R, the probability of transmission of the reservation request packet 102 is lowered. It means that the transmitting station 1, cannot transmit the reservation request packet 102 in some cases. As is known from this, the receiving station 1R perform traffic control of the wireless transmission path 2 according to the transmission probability value P so as to prevent the wireless transmission path 2 from being congested.
Also, if the transmitting station 1T transmits the data packet 104 less often, the valid period VP controlled on the receiving station 1R side accordingly becomes invalid rather soon and thus the bandwidth reserved for the transmitting station 1T is released. Accordingly, the bandwidths of the wireless transmission path 2 can be more effectively utilized.
Still further, in the communication system CS, the transmitting station 1T and the receiving station 1R can each obtain the partner's identifier ID for data communication before going through the data communication phase. Also, the transmitting station 1T judges whether the communication reservation packet 103 is addressed thereto according to the first and second CRC values (see FIG. 12a or 12b), while the receiving station 1R judges whether the data packet 104 is addressed thereto according to the first and second CRC values. In this manner, there is no more need to set the source identifier SID and the destination identifier DID to both the communication reservation packet 103 and the data packet 104. Accordingly, it becomes possible to make the packet length shorter, and thus the bandwidths of the wireless transmission path 2 can be more effectively utilized.
Although the wireless transmission path 2 interconnects the communication stations 1 in the communication system CS, a wired transmission path will do.
When it is known in step S38 in FIG. 6 that the predetermined time TPRE1 is passed, the procedure goes to step S36. However, the lapse of predetermined time TPRE1 is enough for the receiving station 1R to make a judgement that the wireless transmission path 2 has no incoming signal. Therefore, at this point in time, the receiving station 1R may transmit the communication reservation packet 103 to any one of the communication stations 1 for which a bandwidth is reserved.
Still further, in steps S141 and S146 in FIG. 10, if the transmitting station 1T cannot correctly receive the communication reservation packet 103 and the data packet 104 addressed thereto, the procedure goes to steps S146 and S147. However, in steps S141 and S146, the transmitting station 1T may receive the communication reservation packet 103 and the data packet 104 which are not addressed thereto. If this is the case, the possibility for the wireless transmission path 2 being congested is low, therefore the transmitting station 1T may transmit the reservation request packet 102 to a certain communication station 1 when having any data for transmission thereto.
Still further, in this embodiment, the receiving station 1R lengthens the valid period vP on reception of the data packet 104 from the transmitting station 1T in step S65 in FIG. 7. However, the receiving station 1R may transmit, to the transmitting station 1T, the communication reservation packet 103 which the transmitting station 1T can transmit the data packet 104 with the length being relatively longer. In other words, the receiving station 1R may dynamically change the transmission cycle of the communication reservation packet 103.
Still further, in the communication system CS, the receiving station 1R controls reception of the data packet and assignment of bandwidths. However, one of the communication stations 1 may centrally control assignment of the bandwidths of the wireless transmission path 2, and other communication stations 1 may perform data communication therebetween.
In the communication procedure in FIGS. 13 and 14, the case where the transmitting station 1T transmit data to the receiving station 1R is described. However, in the communication system CS, some data may be generated in the receiving station 1R for transmission to the transmitting station 1T while the transmitting station 1T is transmitting data thereto. If this is the case, the transmitting station 1T and the receiving station 1R perform two-way data communication by using the communication procedure as shown in FIG. 15. Next below, similarly to the cases in FIGS. 13 and 14, the communication station 1a presumably operates as the receiving station 1R, and the communication station 1b as the transmitting station 1T.
The communication station 1a transmits the request inquiry packet 101 in a similar manner to sequences Seq111 and Seq112 (FIG. 15; sequence Seq211), and receives the reservation request packet 102 from the transmitting station 1b as a reply (sequence Seq221). The communication station 1a disassembles the reservation request packet 102 and then reserves a bandwidth for the communication station 1b. Thereafter, the communication station 1a transmits the communication reservation packet 103 to the communication station 1b in a similar manner to the sequences Seq131 and Seq132 (FIG. 15; sequences Seq23, and Seq232). The communication station 1b assembles the data packet 104 in response to the communication reservation packet 103 as in sequences Seq141 and Seq142 for transmission to the communication station 1a (sequences Seq241 and Seq242).
After receiving the data packet 104 transmitted in sequence Seq242, the communication station 1a lengthens the valid period VPb of the communication station 1b (FIG. 7; step S65). If the communication station 1a does not yet transmit the communication reservation packet 103 for the required number of pieces, the procedure goes to step S6 in FIG. 5 (that is, step S61 in FIG. 7). Assuming that the identifier ID of the communication station 1b is again selected (step S61), the communication station 1a decides if having any data for transmission thereto (step S62). If any, the communication station 1a assembles the data packet 104 for transmission thereto (sequence Seq233).
Thereafter, the communication station 1a waits for the data packet 104 from the communication station 1b.
After transmitted the data packet 104 to the communication station 1a in sequence Seq242, the communication station 1b is again waiting for the communication reservation packet 103 addressed thereto (steps S141 and S147 in FIG. 10). Then, the communication station 1b detects, receives, and disassembles the packet on the wireless transmission path 2 after sequence 233 so as to determine if the received packet is the communication reservation packet 103 (step S141). Since the communication station 1b notices, over disassembly, that the packet type T included therein does not indicate the communication reservation packet 103, the procedure goes to step S146.
Thereafter, the communication station 1b decides that the received packet is the data packet 104 with the help of packet type T, and then further disassembles the packet to extract the data block DB therefrom (step S146). The procedure then goes to step S143 and onwards, and accordingly the communication station 1b assembles the data packet 104 for transmission to the communication station 1a responding to the data packet 104 therefrom (step S143, sequence Seq243). From then and onward, the communication station 1, and 1b exchange the data packet 104 therebetween.
While the invention has been described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is understood that numerous othermodifications and variations can be devised without departing from the scope of the invention.

## Claims

1. A communication system in which a transmitting station and a receiving station are communicably connected through a transmission path, and the receiving station reserves a bandwidth used in data communication for the transmitting station in advance, wherein
said transmitting station transmits a reservation request packet for bandwidth reservation to said receiving station when data to be transmitted is generated, 
said receiving station reserves the bandwidth in response to the reservation request packet from said transmitting station, and transmits a communication reservation packet for informing said transmitting station of the reserved bandwidth, 
said transmitting station creates a data packet according to the generated data, and transmits the created data packet through the bandwidth informed by the communication reservation packet from said receiving station, 
said receiving station stores a valid period of the bandwidth reserved for said transmitting station, and voluntarily and repeatedly transmits the communication reservation packet to said transmitting station during the stored valid period, 
an initial value of the valid period stored for said transmitting station is predetermined, and 
said receiving station further 
shortens the stored valid period with given timing, 
lengthens the stored valid period on reception of the data packet from said transmitting station, 
deletes the valid period when the valid period is equal to a predetermined reference value, and 
voluntarily and repeatedly transmits the communication reservation packet to said transmitting station as long as the valid period is stored.

2. The communication system as claimed in claim 1, wherein said transmitting station further sets an identifier assigned thereto to the reservation request packet, and
said receiving station further 
stores the identifier set to the reservation request packet transmitted from said transmitting station together with the initial value of the valid period, and 
when deletes the valid period, deletes the stored identifier together therewith.

3. The communication system as claimed in claim 1, wherein said receiving station further changes a time interval between two communication reservation packets according to the valid period.

4. A communication system in which a transmitting station and a receiving station are communicably connected through a transmission path, and the receiving station reserves a bandwidth used in data communication for the transmitting station in advance, wherein
said transmitting station transmits a reservation request packet for bandwidth reservation to said receiving station when data to be transmitted is generated, 
said receiving station reserves the bandwidth in response to the reservation request packet from said transmitting station, and transmits a communication reservation packet for informing said transmitting station of the reserved bandwidth, 
said transmitting station creates a data packet according to the generated data and transmits the created data packet through the bandwidth informed by the communication reservation packet from said receiving station, 
said receiving station stores a valid period of the bandwidth reserved for said transmitting station, and voluntarily and repeatedly transmits the communication reservation packet to said transmitting station during the stored valid period, 
said receiving station further transmits, with given timing, a request inquiry packet for allowing said transmitting station to transmit the reservation request packet, and 
said transmitting station further transmits the reservation request packet in response to the request inquiry packet transmitted from said receiving station.

5. The communication system as claimed in claim 4, wherein said receiving station further sets, to the request inquiry packet, a probability that said transmitting station can transmit the reservation request packet, and
said transmitting station further transmits the reservation request packet according to the probability value included in the request inquiry packet transmitted from said receiving station.

6. The communication system as claimed in claim 5, wherein, when said receiving station detected a communication collision on said transmission path, the probability value set to the request inquiry packet is relatively low.

7. The communication system as claimed in claim 5, wherein, when said receiving station correctly received the reservation request packet from said transmission path, the probability value set to the request inquiry packet is relatively high.

8. The communication system as claimed in claim 5, wherein, when no signal arrives the receiving station from said transmission path for a given time period, the probability set to the request inquiry packet is relatively high.

9. A communication system in which a transmitting station and a receiving station are communicably connected through a transmission path, and the receiving station reserves a bandwidth used in data communication for the transmitting station in advance, wherein
said transmitting station transmits a reservation request packet for bandwidth reservation to said receiving station when data to be transmitted is generated, 
said receiving station reserves the bandwidth in response to the reservation request packet from said transmitting station, and transmits a communication reservation packet for informing said transmitting station of the reserved bandwidth, 
said transmitting station creates a data packet according to the generated data, and transmits the created data packet through the bandwidth informed by the communication reservation packet from said receiving station, 
said receiving station stores a valid period of the bandwidth reserved for said transmiting station, and voluntarily and repeatedly transmits the communication reservation packet to said transmitting station during the stored valid period, and 
said receiving station further changes a time interval between two communication reservation packets according to a transfer rate required by said transmitting station.

10. A communication system in which a transmitting station and a receiving station are communicably connected through a transmission path, and the receiving station reserves a bandwidth used in data communication for the transmitting station in advance, wherein
said transmitting station transmits a reservation request packet for bandwidth reservation to said receiving station when data to be transmitted is generated, 
said receiving station reserves the bandwidth in response to the reservation request packet from said transmitting station, and transmits a communication reservation packet for informing, said transmitting station of the reserved bandwidth, 
said transmitting station creates a data packet according to the generated data, and transmits the created data packet through the bandwidth informed by the communication reservation packet from said receiving station, 
said receiving station stores a valid period of the bandwidth reserved for said transmitting station, and voluntarily and repeatedly transmits the communication reservation packet to said transmitting station during the stored valid period, and 
when no signal arrives the receiving station from said transmission path for a given time period, said receiving station further judges that the communication reservation packet can be transmitted.

11. A communication system in which a transmitting station and a receiving station are communicably connected through a transmission path, and the receiving station reserves a bandwidth used in data communication for the transmitting station in advance, wherein
said transmitting station transmits a reservation request packet for bandwidth reservation to said receiving station when data to be transmitted is generated, 
said receiving station reserves the bandwidth in response to the reservation request packet from said transmitting station, and transmits a communication reservation packet for informing said transmitting station of the reserved bandwidth, 
said transmitting station creates a data packet according to the generated data, and transmits the created data packet through the bandwidth informed by the communication reservation packet from said receiving station, 
said receiving station stores a valid period of the bandwidth reserved for said transmitting station, and voluntarily and repeatedly transmits the communication reservation packet to said transmitting station during the stored valid period, and 
when no signal arrives the receiving station from said transmission path for a given time period, said transmitting station further judges that the reservation request packet can be transmitted.

12. A communication system in which a transmitting station and a receiving station are communicably connected through a transmission path, and the receiving station reserves a bandwidth used in data communication for the transmitting station in advance, wherein
said transmitting station transmits a reservation request packet for bandwidth reservation to said receiving station when data to be transmitted is generated, 
said receiving station reserves the bandwidth in response to the reservation request packet from said transmitting station, and transmits a communication reservation packet for informing said transmitting station of the reserved bandwidth, 
said transmitting station creates a data packet according to the generated data, and transmits the created data packet through the bandwidth informed by the communication reservation packet from said receiving station, 
said receiving station stores a valid period of the bandwidth reserved for said transmitting station, and voluntarily and repeatedly transmits the communication reservation packet to said transmitting station during the stored valid period, and 
said transmitting station further measures a lapse of time after transmitted the data packet, and 
when the lapse oftime becomes equal to a reference value relevant to the valid period, judges that the reservation request packet can be transmitted.

13. A communication system in which a transmitting station and a receiving station are communicably connected through a transmission path, and the receiving station reserves a bandwidth used in data communication for the transmitting station in advance, wherein
said transmitting station transmits a reservation reguest packet for bandwidth reservation to said receiving station when data to be transmitted is generated. 
said receiving station reserves the bandwidth in response to the reservation request packet from said transmitting station, and transmits a communication reservation packet for informing said transmitting station of the reserved bandwidth, 
said transmitting station creates a data packet according to the generated data, and transmits the created data packet through the bandwidth informed by the communication reservation packet from said receiving station, 
said receiving station stores a valid period of the bandwidth reserved for said transmitting station, and voluntarily and repeatedly transmits the communication reservation packet to said tranmitting station during the stored valid period, and 
said transmitting station determines numbers of the communication reservation packets to be transmitted, and transmits the communication reservation packets according to the determined numbers.